1. Field of the Invention
The present invention relates to a method of coring a crustal core samples used for various researches, for example, biological researches on subsurface microorganisms or the like in a crustal core, and chemical, physical and geological researches, and a flow-able coating material for coring a crustal core sample.
2. Description of the Background Art
In recent years, researches on crustal interiors have been advanced, and the presence of the subsurface microorganisms under a deep-depth, high-temperature and high-pressure environment in a crustal interior has been reported. According to researches on the subsurface microorganisms in a deep sphere composed of these subsurface microorganisms, there is a possibility that important findings, for example, elucidation of influences by material conversion and mass transfer in a deep geological environment, elucidation of origin of life in the primitive earth and evolution thereof, or development of drugs and novel materials may be obtained. Further, chemical researches, physical researches or geological researches in such a deep-depth crustal interior are advanced from various points of view.
A crustal core sample used for such various researches as described above can be taken with comparative ease from the crust at the depth closer to mantle by drilling a submarine crust by means of, for example, a drill ship.
As an example of a method of conducting the drilling using the drill ship, for example, a riser drilling method has been generally known. In this method, a drill pipe extending from the drill ship to the sea bottom is rotated to drill the crust by means of a drill bit provided on the tip thereof and at the same time, a fluid (hereinafter also referred to as “working fluid”) for drilling work, such as so-called drilling mud or sea water, the specific gravity, viscosity, chemical composition, etc. of which have been adjusted according to the condition of the crust drilled, is fed to the drill bit to remove drill debris, and to protect and stabilize a side wall of the drill hole. Since the working fluid is fed through a circulating channel in the riser drilling method, the fluid is also referred to as “circulating fluid”.
A crustal core sample taken by such a method has a great possibility that the state of the sample present in the crust as it is may be lost by an influence exerted from the outside during the coring operation, for example, by contact of the working fluid containing drill debris. In such a case, there is a possibility that the crustal core sample cored may become a sample lost its important information for intended researches.
In order to overcome with such a problem, there is disclosed a method of coring a crustal core sample, that an outer surface of the crustal core sample is coated with a flow-able coating material composed of gel or the like when the crustal core sample is taken, thereby obtaining the crustal core sample in a state that its mechanical structure or tissue has been protected from the outside (see, for example, U.S. Pat. No. 5,482,123).
As described below, it is also known to use an antimicrobial substance as a flow-able coating material, thereby taking a crustal core sample in a state protected from contamination with, for example, adventitious nonindigeneous microorganisms (see, Japanese Patent Application Laid-Open No. 2002-228558).
FIG. 1 illustrates a case where a sea bed crust is drilled by means of a drill ship in accordance with the riser drilling method.
In this drilling method, a drilling operation is conducted by a riser drilling system provided on a drill ship 10 on the surface 13 of the sea. In the riser drilling system, a riser pipe 20 extending downward from the drill ship 10 into the sea to connect between the drill ship 10 and a sea floor 15 is provided, and a drill pipe 21 is arranged within this riser pipe 20. This drill pipe 21 is so constructed that its upper end is connected to a power swivel 11 that is a rotating drive mechanism on the drill ship 10, and its lower part enters the crust 16 through a blowout-preventing device 14. A drill bit 30 is provided at the lower end of the drill pipe 21.
The drill ship 10 is generally equipped with an automatic ship position keeping system constructed by correlating a plurality of thrusters 12a, 12b and 12c provided on the bottom of the ship, a differential global positioning system (DGPS) making good use of, for example, an artificial satellite, and the like. According to this automatic ship position keeping system, the position of the ship can be held within a region of a small radius centering an intended drill hole in the sea floor 15 without being affected by the wind, the tidal current and the like even in the open sea.
The drill bit 30 is so constructed that a plurality of semispherical cutter parts each protruding downward are formed at a lower end of an outer barrel 23 (see FIG. 11) so as to stand in its peripheral direction, and a plurality of cutter elements 31 (see FIG. 11) are fixed to each of the cutter parts.
The drill bit 30 is rotated through the drill pipe 21 by the power swivel 11, whereby the crust 16 is drilled from the sea floor 15, and the lower end of the drill pipe 21 goes down in the crust 16. At this time, a working fluid composed of drilling mud, seawater or the like is fed to the drill bit 30 through the drill pipe 21 in the riser pipe 20. A plurality of casing pipes 17 different in length from each other provided at the lower part of the blowout-preventing device 14 are inserted according to the depth of the drilling, whereby collapse of the wall surface in the drill hole is prevented.
Numbers of safety valves for pressure relief are provided in the blowout-preventing device 14, and the pressure within the drill hole is controlled by these safety valves, whereby rapid blowout of high-pressure hydrocarbon gases, interstitial water within the crust and/or the like is controlled to surely continue a safe drilling process.
FIG. 2 is a partial sectional view illustrating details of compositional units making up a riser pipe together with a section of a main pipe, taken along its axis, in a state that a drill pipe has been inserted therein.
As illustrated in FIG. 2, the riser pipe 20 is constructed by the main pipe 22 and a kill & choke line 27 provided independently of the main pipe 22, and a double-piped structure is formed by the main pipe 22 and the drill pipe 21 arranged in the main pipe 22. A circulating fluid-running channel 24, through which the working fluid is fed, is formed by an internal space of the drill pipe 21. Through this internal space, various devices, for example, a mechanism forming a crustal core sampler, and the like, are guided to the drill hole. On the other hand, a circulating channel, through which the working fluid is returned back to the drill ship 10, is defined by an annular channel 25 formed between an inner peripheral wall surface of the main pipe 22 and an outer peripheral surface of the drill pipe 21.
More specifically, the working fluid is fed to the drill bit 30, ejected within the drill hole from working fluid-ejecting openings provided at lower end of the drill bit 30 and then circulated through the annular channel 25. This working fluid is a fluid the specific gravity, viscosity, chemical composition and the like of which have been adjusted according to, for example, the geology of the crust. For example, that obtained by mixing various modifiers into muddy water available in a drilling site may be used.
Incidentally, the necessary lengths of the main pipe 22 and the drill pipe 21, and increases thereof are actually achieved by successively joining a great number of respective elements thereof to one another as needed. In FIG. 2, reference numeral 28 indicates a line holder.
The above-described riser drilling method has such merits as described below, whereby a drilling work can be stably conducted.
(1) Removal of Drill Debris:
Drill debris collected on the bottom of the drill hole is conveyed to the drill ship 10 through the annular channel 25 by the working fluid ejected from the drill bit 30.
(2) Protection and Stabilization of Wall Surface of Drill Hole:
The viscous component in the working fluid ejected from the drill bit 30 adheres to the wall surface of the drill hole to form a thin protective film 18 (cf. FIG. 5), whereby collapse of the wall surface in the drill hole is prevented.
The specific gravity in the composition of the working fluid is adjusted, whereby the equilibration of pressure against the formation pressure in a deep depth can be conducted, and an effect of preventing a fluid in the formation from penetrating into the drill hole is brought about.
(3) Cooling and Lubrication of Drill Bit:
The drill bit 30 is cooled by contacting of the working fluid with its surface to prevent it from being excessively heated by gradually rising crustal heat, and lubricating effect is achieved between the drill bit 30 and the crust, so that the degree of friction in the drill bit 30 is lowered to lessen the abrasion of the drill bit 30. (4) The constitutive substances and the like of the drill debris contained in the working fluid sent on to the drill ship 10 are successively analyzed and monitored, whereby the geological condition of the crust, to which drilling is being conducted at this very moment, is easy to be always confirmed and grasped.
As understood from the above fact, the drill pipe 21 and drill bit 30 for drilling the crust 16 are required to permit feeding and ejecting the working fluid from the tip parts thereof, and the so-called coring drill bit having an opening at a central part along a rotating axis thereof is preferably used.
A case where a crustal core sample is cored by the riser drilling method using a conventional crustal core sampler disclosed in U.S. Pat. No. 5,482,123 is then specifically described.
FIGS. 11 and 12 are sectional views illustrating the states, in terms of sections, of a drill pipe and a drill bit in a drilling work. FIG. 11 illustrates a state right after drilling is started, while FIG. 12 illustrates a state that the drilling has been advanced.
In the crustal core sampler in this example, a pipe-like inner barrel 60 is arranged, in a mode that a thrust bearing (not illustrated) is intervened, in an outer barrel 23 making up a drill pipe 21 and provided with a drill bit 30 at the tip thereof.
At a lower end of the inner barrel 60, a disk-like flow-able coating material-ejecting opening member 62 is arranged in a state that liquid-tightness is retained so as to close the opening of the inner barrel through a ring-like sealing member 61, and relatively movably in a vertical direction within the inner barrel 60.
In this flow-able coating material-ejecting opening member 62, is formed flow-able coating material-ejecting holes 68 linking the interior of the inner barrel 60 with the outside and extending through in a vertical direction and is provided an opening and closing valve 65 for opening and closing the flow-able coating material-ejecting holes 68. In other words, the opening and closing valve 65 is constructed by a valve body member 64 arranged vertically movably on the inner side (upper surface side) of the flow-able coating material-ejecting opening member 62, a connecting rod 63 extending slidably in a vertical direction through the flow-able coating material-ejecting opening member 62 and a working disk 66 provided at a lower end of the connecting rod 63 and located on the outer side (lower surface side) of the flow-able coating material-ejecting opening member 62. The connecting rod 63 has a length longer than the thickness in the vertical direction of the flow-able coating material-ejecting opening member 62. A flow-able coating material 67 is filled in the interior of the inner barrel 60.
In the riser drilling method using the crustal core sampler having the structure described above, as illustrated in FIG. 11, the outer barrel 23 in a state rotated about an axis of the barrel, and the inner barrel 60 retained in a standstill state in this rotational direction by the thrust bearing which is not illustrated go down from the sea floor 15 when drilling of the crust 16 is started, whereby the working disk 66 provided at the lower end in the connecting rod 63 is pushed up relatively upward by the sea floor 15, and the valve body member 64 is separated from the inner surface (upper surface) of the flow-able coating material-ejecting opening member 62 through the connecting rod 63 to open the flow-able coating material-ejecting holes 68. As a result, a state that the interior of the inner barrel 60 is linked with the outside is created, and the flow-able coating material 67 in the inner barrel 60 is ejected to the outside through the flow-able coating material-ejecting holes 68.
As illustrated in FIG. 12, a columnar crustal core portion P formed by drilling the periphery thereof with the downward movement of the outer barrel 23 and inner barrel 60 by the progress of the drilling, enters the interior of the inner barrel 60 from the central opening of the drill bit 30 while forming a narrow annular gap G between the outer peripheral surface of the columnar crustal core portion P and the inner peripheral wall surface of the inner barrel 60, and moreover the flow-able coating material-ejecting opening member 62 is moved relatively upward within the inner barrel 60 together with the columnar crustal core portion P gradually grown while retaining the state that the flow-able coating material-ejecting holes 68 has been linked with the interior.
As a result, the flow-able coating material 67 is ejected into the annular gap G through the flow-able coating material-ejecting holes 68 and adheres to the outer peripheral surface of the columnar crustal core portion P gradually grown.
The columnar crustal core portion P entered into the inner barrel 60 is broken at a lower portion thereof and taken. This crustal core portion is recovered as a crustal core sample with the inner barrel 60 on the drill ship 10 through the interior of the drill pipe 21 by a wire or the like.
However, it becomes clear that it is not possible to sufficiently and surely prevent the obtained crustal core sample from being contaminated by adventitious microorganism even in the case where the flow-able coating material is used in a method of coring a crustal core sample utilizing the working fluid such as mud water. This is because that although a coating material layer is formed on the outer surface of the cored crustal core sample, the contaminants originated from working fluid are adhered onto the surface of the crustal core sample, since the working fluid is contacted to the surface before the coating material is adhered. In other words, it is thought that it is because, since the working fluid is that composed of a large quantity of microscopic particles having the particle diameter of, for example, at most 1 μm contained in water as colloidal particles, contaminants such as adventitious microorganism and the like are adhered on to the outer surface of the crustal core sample being formed, by being mediated by the water and the microscopic particles of the working fluid, and furthermore, the contaminants enter into the inside of the surface layer.
Especially, when the crustal substance which is an object of drilling is comparatively soft rock, the columnar crustal core portion obtained becomes small in diameter because of the vibration of the drill bit in a radial direction during the drilling. As a result, the annular gap G in the inner barrel becomes larger and it allows a large quantity of working fluid to enter into the annular gap G, thereby a possibility of adhesion of the contaminants to the crustal core sample to be obtained becomes high.